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I'm fascinated with seasonal heat storage using large underground water tanks. Apparently one drains the heat in winter, and dumps heat during the summer?

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As @blahlabs notes in peer comment sand batteries / heating buried dirt works better than heating water for seasonal power storage and smoothing.

In simple terms there's better efficiency and ease of use from having a higher delta (temperature difference) and dirt / sand / salts heated to 600C are significantly hotter than water at 100C.

Once water turns to steam drama and expenses climb.

Makes perfect sense. Now I wonder why these big water batteries were built in the first place.

Sand batteries are a similar concept, with the advantage of being able to store at over 100°C. I believe they can store heat for months.

https://polarnightenergy.com/news/worlds-largest-sand-batter...

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